<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<style>
    .box {
        display: flex;
        width: 500px;
        border: 1px solid red;
    }
    .box div{
      border: 1px solid black;
    }
    .div1{
        flex: 1 1 auto;
    }
    .div2{
        flex: 1 1 auto;
    }
    .div3{
        flex: 1 1 auto;
    }
</style>
<div class="box">
  <div class="div1">One</div>
  <div class="div2">Two</div>
  <div class="div3">Three
    <br>has
    <br>extra
    <br>text
  </div>
</div>
</body>
</html>
